1. Field of the Technology
The present technology relates to a punching apparatus for performing a paper finishing operation disposed along a transport path used for transporting image-formed (printed) paper to a stacking location in a discharge portion.
2. Description of the Related Art
When images are printed on transported paper in a conventional image forming apparatus, image information is transferred onto the paper in a transfer portion by rendering electrostatic latent images formed on an electrostatic latent image carrier (photosensitive drum) visible using a developer (toner) and transporting the paper to the location of the transfer process using timing that ensures coordination between the leading edge of the paper and the leading edge of the image information on the photosensitive drum.
In recent years, following the development of color image forming apparatuses, and the increase in the printing speed of image forming apparatuses, highly efficient transfer techniques have been required in the transfer process. At present, methods frequently used in the transfer process include methods such as “corona charger”, “roller transfer”, “brush transfer”, “belt transfer”, and the like, with each of these methods employing a technique, in which a toner image electrically attracted to the surface of a photosensitive drum is transferred to paper by applying, to the respective members, a transferring electric field (of 1-3 kV or so) having a polarity opposite that of the electrostatic polarity of the developer (toner). The paper, to which such a transferring electric field is applied, is charged by the electric field that transfers toner images from the photosensitive drum to the paper.
Moreover, the transported paper are tribocharged as a result of rubbing against a number of transport rollers, paper guides, etc. disposed between the paper feed portion and the discharge portion, such that it is common for the discharged paper to carry approximately 1-2 kV of static electricity when printing is complete. When multiple sheets of the thus electrostatically charged paper are discharged into a discharge tray portion, there is a chance that repulsing electric fields may be generated between the sheets of the paper and may bring about a stacking failure in the discharge tray portion.
Accordingly, to eliminate such problems, it has been proposed to position a destaticizing brush, which is an electroconductive brush, in the vicinity of the discharge rollers (for example, see JP H02-23384A (hereinafter referred to as “Patent Document 1”)).
Moreover, recently, many apparatuses have been developed that employ the “belt transfer” method, in which a transfer belt is utilized to reliably transport transported paper to the transfer portion, where the transfer process is performed. In the belt transfer method, an endless belt with a predetermined resistance value is supported by multiple rollers, and a transfer region, which is termed “transfer nip”, is formed between the photosensitive drum and one of the supporting rollers or a roller between the supporting rollers.
In the belt transfer method used to carry out such a transfer process, the number of electric fields applied to the transfer belt is larger in comparison with conventional methods such as “corona charger”, “roller transfer”, and “brush transfer”. Namely, it requires an “attracting field”, which attracts transported paper to the transfer belt, a “transfer field”, which is indispensable for the transfer process, a “separating field”, which separates paper from the transfer belt in order to smoothly transport the adhered paper bearing the transferred images to the next process, etc.
Thus, in an image forming apparatus employing the belt transfer method in the transfer process, in the transfer process, paper are subjected to the influence of the above-described multiple electric fields as well as to the tribocharging by transport rollers etc. along the transport path. Moreover, in a printing mode (i.e. color printing mode) that requires not one pass, but two or more passes along the transport path during printing, paper are affected by the above-mentioned various electric fields as many times as the paper goes through the transfer process and along the transport path.
Table 1 lists results obtained by measuring the charge of transported paper upon completion of printing in such various printing modes.
TABLE 1Electrostatic Charge of Transported PaperElectrostatic Charge ofPaper At Time of Discharge(kV/sheet) (Paper Type: A4)Pseudo Printing (duplex1.0-1.5printing) (Printing density: 0%)Monochromatic Printing2.0-3.5(duplex printing)Color Printing4.0-6.5(duplex printing)
As can be seen from Table 1, color printing produces incomparably higher levels of electrostatic charge in paper than in case of pseudo printing or monochromatic printing.
As concerns the paper discharged in such a state, as a way of making image forming apparatuses multi-functional, a growing number of recently developed apparatuses are equipped with a finishing unit, in which printed paper is subjected to a finishing process. Stapling, punching, and saddle-stitching operations including bookbinding, as well as filing, etc. are carried out during the finishing process.
Punch waste is produced from the punched paper when paper electrostatically charged in the above-described manner undergo punching during the finishing process. In this case, when the punch waste does not carry static electricity, it falls naturally into a holding container for punch waste disposed below, due to its own gravity etc. and accumulates in it in a natural manner. However, punch waste that carries static electricity does not fall naturally into the collecting container and sticks to the surface of the walls etc. of the container due to the action of static electricity.
The resulting state is illustrated in FIG. 17. As shown in FIG. 17, punch waste 130 adhered to a fullness detecting sensor 102 disposed on the wall etc. of the container leads to frequent misdetection by the fullness detecting sensor 102, which detects that the container is full despite the fact that the amount of waste collected in a collecting container 63 does not make it full. Moreover, blocking phenomena (bridging phenomena) may occur as a result of contact between chads 130 adhered to the walls of the container and voids 150 may also be created inside the collecting container 63. The problem arising in such a case is that the fullness detecting sensor 102 may end up detecting fullness before the appropriate amount of waste is collected in the container (before it is full) because of the punch waste 130 piling up on top of them. In addition to that, another problem that may arise is that the punch waste 130 carrying static electricity may be scattered outside the container and may stick to the inside of the apparatus when the collecting container is taken out and put in.
Accordingly, technologies have been proposed for eliminating such problems (for example, see JP H11-255417A (hereinafter referred to as “Patent Document 2”) and JP 2003-232671A (hereinafter referred to as “Patent Document 3”)).
As described in Patent Document 2, a punch waste storage container is vibrated using a punch waste vibrator apparatus in order to flatten the pile of punch waste. Moreover, Patent Document 3 describes providing support means for supporting, in a vertically movable manner, punch waste collecting means for receiving punch waste, and detection means for detecting the lowered position of the punch waste collecting means that descends as the weight of the punch waste collected thereon increases, and, after the punch waste collecting means has descended to a predetermined position, detecting that the punch waste collecting means is fully loaded with punch waste.
The technologies described in the above-mentioned Patent Document 1, 2, etc. are effective when the tribocharge of the transported paper is small, such as when the image forming apparatus is a low-speed apparatus, when the printing mode is monochromatic printing, etc. In other words, a corresponding effect can be expected in case the tribocharge is 1-2 kV or so, as described in the above-mentioned conventional technologies.
However, as described above, image forming apparatuses have increased in speed in recent years, and, moreover, when the belt transfer method is used in the transfer process, as shown in Table 1, the electrostatic charge of the paper increases and even if the punch waste storage container is vibrated as described in Patent Document 2, it is impossible to throw off all the chads adhered to the container walls etc.
Moreover, when paper are discharged to the discharge tray, their static electricity is removed because according to the technology described in Patent Document 1a destaticizing brush is disposed on the downstream side of the discharge rollers. However, it is still a problem that, when a finishing process is added, strong shearing forces generated by the action of the hole-punching punch during the punching operation produce a tribocharge in the punch waste, with the punch waste adhering to the container walls etc. and causing the fullness detecting sensor to erroneously detect fullness.
In addition, because the technology described in Patent Document 3 detects substantially the weight of the punch waste collecting means (punch waste collecting container) alone, the possibility of fullness misdetection is eliminated even if the punch waste does carry static electricity and adheres to the container walls etc. However, the problem is that, unlike a conventional fullness detecting sensor, this technology requires a mechanism for vertically moving the punch waste collecting means and a detection sensor for detecting the descent of the punch waste collecting means, which makes the construction used for conducting the punching process more complicated and at the same time ends up increasing component cost. Moreover, yet another problem is that apparatus miniaturization will be limited, too, because its construction becomes more complicated.